Air cavity packages for RF power applications include an RF power transistor die with the source terminal attached to a metal flange and a ceramic (alumina) based window frame for isolating the gate and drain leads of the power transistor from the source-connected flange. Such packages are relatively expensive and have poor CTE (coefficient of thermal expansion) matching. Standard RF power packages are often built with either CPC (copper, copper-molybdenum, copper laminate flange), CuW or CuMo flanges all having a CTE closely matched to ceramic. However, the CTE of the flange tends to be quite lower than the system cooling blocks/coins which are soldered onto the flange. CTE mismatch between the flange and the cooling blocks/coins creates solder fatigue, component fracture and bowing issues. Also, there is a CTE match with the leads so that the window frame and corresponding leads are CTE matched with the customer PCB (printed circuit board).
In addition, conventional RF power packages have gate and drain leads attached to and protruding outward from the ceramic window frame. The leads provide input and output terminals to the package. However, the leads typically comprise Alloy42, Kovar, copper or similar materials and are typically 3-7 mil thick. Such leads are soft and readily bend in the region unsupported by the window frame, creating a problem with the seating plane height for soldering. In addition, conventional metal/ceramic packages transmit RF energy through high loss Ni/Pd/Au or Ni/Au plating due to the skin effect in RF. Another approach is a plastic/molded LCP (liquid crystal polymer) window frame in place of a ceramic window frame. However, LCP window frame type packages have an inherent gross leak issue which results in decreased reliability and higher yield loss. A more reliable, lower cost air cavity RF power package is therefore desirable.